Just start where you are right now. Read down the replies. If you see one you wish to reply to, post the reply. Then hit your back button which will take you back to the post you replied to, and you can continue on.
Or, you can just read and periodically hit the refresh button.
It takes a while to get the hang of it. I am a quick typist, so it is easier for me. Don't leave, though. You'll get the hang of it!
Thanks for the advice on posting. It's like watching double-dutch jump rope and wondering how the heck you are going to get in!